1. Field of the Invention
The present invention relates to solid-state image pickup devices, such as complementary metal-oxide semiconductor (CMOS) image sensors.
2. Description of the Related Art
Solid-state image pickup devices are used for the purpose of recording images and for various other purposes, such as image recognition. In particular, when a solid-state image pickup device is used as an image sensor for image recognition of a moving object, output signals of two consecutive frames are compared with each other so that the direction and speed of the moving object in the frames are recognized. Since an object moving at very high speed may pass through the field of view of a solid-state image pickup device and disappear from the field of view in a moment, the moving object must be captured in at least two frames in a fraction of a second. In this case, high-speed frame reading (high frame rate) is required for the solid-state image pickup device. A solid-state image pickup device for detecting the movement of a moving object is described, for example, in Japanese Unexamined Patent Application Publication No. 11-8805.
Although various procedures for increasing the frame reading speed have been suggested, a further increase in the frame reading speed is strongly desired.